Quiznetik

Testing and Commissioning of Electrical Equipment’s | Set 2

1. What is the actuating quantity for the relays?

A. Magnitude

B. Frequency

C. Phase angle

D. All of these

Correct : D. All of these

2. Which among these are the main characteristics of a fuse element?

A. Low melting point

B. High conductivity

C. Least deterioration due to oxidation

D. All of the above

Correct : D. All of the above

3. What is the making capacity of the circuit breaker?

A. Less than the asymmetrical breaking capacity of the breaker

B. Greater than the asymmetrical breaking capacity of the breaker

C. Equal to the asymmetrical breaking capacity of the breaker

D. Equal to the symmetrical breaking capacity of the breaker

Correct : B. Greater than the asymmetrical breaking capacity of the breaker

4. In a circuit breaker the contact space is ionised by what?

A. Field emission from the contact surface.

B. Thermal emission from the contact surface.

C. Thermal ionisation of gas.

D. All of above.

Correct : C. Thermal ionisation of gas.

5. A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breaking current?

A. 1200 A

B. 3600 A

C. 35 kA

D. 104.8 kA

Correct : C. 35 kA

6. What should be the value of fusing factor?

A. Equal to zero

B. Equal to one

C. Less than one

D. More than one

Correct : C. Less than one

7. What is the relation between the fusing current and the diameter of the wire?

A. I = k d3

B. I = k d3/2

C. I = k d2

D. I = k d2/3

Correct : B. I = k d3/2

8. The making and breaking currents of a 3 phase ac circuit breakers in power systems are respectively in ________form.

A. rms value, rms value

B. instantaneous value, rms value

C. rms value, instantaneous value

D. instantaneous value, instantaneous value

Correct : D. instantaneous value, instantaneous value

9. Why is an isolator installed?

A. To isolate one portion of the circuit from another

B. As an substitute for the circuit breaker

C. It used on either sides of the circuit breaker

D. Both (a) and (c)

Correct : A. To isolate one portion of the circuit from another

10. Assertion (A): In comparison to making capacity of a circuit breaker its breaking capacity is normally higher. Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10-6 MVA

A. Both A and R are true and R is the correct explanation of A

B. Both A and R are true and R is not the explanation of A

C. A is true but R is false

D. A is false but R is true.

Correct : D. A is false but R is true.

11. What is the cut off current in the fuse?

A. Maximum value actually reache(D)

B. Rms value actually reache(D)

C. Average value actually reach

Correct : A. Maximum value actually reache(D)

12. Which circuit breaker is preferred to be installed in extra high voltage AC system?

A. Bulk oil type circuit breaker

B. Air blast circuit breaker

C. SF6 circuit breaker

D. Vacuum circuit breaker

Correct : C. SF6 circuit breaker

13. A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?

A. 35 kA

B. 49 kA

C. 70 kA

D. 89 kA

Correct : D. 89 kA

14. A fuse wire of circular cross section has a radius of 0.8mm. The wire blows off at a current of 9(A) What will be the radius of the wire that will blow off at a current of 1A?

A. 0.2 mm

B. 0.18 mm

C. 0.28 mm

D. 0.3 mm

Correct : B. 0.18 mm

15. Which among these tests are performed to check the nation or international standards?

A. Type test.

B. Production tests.

C. Site checks.

D. All of the above.

Correct : A. Type test.

16. Refer to the following facts to answer the question A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to a bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0.01 μ F. What is the frequency of oscillations?

A. 10000 Hz

B. 12500 Hz

C. 12628 Hz

D. 13265 Hz

Correct : C. 12628 Hz

17. What is switchgear?

A. An apparatus used for switching, controlling and protecting the electrical circuits and equipments.

B. It detects the faults only.

C. It corrects the faults only.

D. All of the above.

Correct : D. All of the above.

18. What is / are the main disadvantage / s of using oil as the quenching medium in the circuit breakers?

A. Need periodical replacement.

B. Risk of formation of explosive mixture with air.

C. Possibility of causing fire hazards.

D. All of the above.

Correct : D. All of the above.

19. Which of the following circuit breakers has the lowest operating voltage?

A. SF6 circuit breaker

B. Air break

C. Air blast

D. Minimum oil circuit breaker

Correct : B. Air break

20. The most efficient torque producing actuating structure for the induction type relays is

A. Shaded pole structure

B. Watt hour meter structure

C. Induction cup structure

D. Single induction loop structure

Correct : C. Induction cup structure

21. Plug setting of a electromagnetic relay can be altered by varying

A. Number of ampere turns

B. Air gap of magnetic path

C. Adjustable back stop

D. None of these

Correct : A. Number of ampere turns

22. Which material is used for the manufacture of bus bars?

A. Aluminium rods.

B. Copper rods.

C. Any conducting material.

D. Made of silver.

Correct : B. Copper rods.

23. Which device sends the information to the circuit breaker to interrupt the circuit in case of fault?

A. Switch

B. Relay

C. Circuit breaker itself does this function.

D. Fuse.

Correct : B. Relay

24. When does the circuit breaker operate in the line?

A. When power is to be supplie(D)

B. When the line is to be teste(D)

C. Whenever the fault occurs in the line.

D. Whenever the switch and the relay has to be operate(D)

Correct : C. Whenever the fault occurs in the line.

25. What is the primary principle of a fuse?

A. Open the circuit.

B. Protect the appliance.

C. Protect the line.

D. Prevent excess current from flowing into the line.

Correct : D. Prevent excess current from flowing into the line.

26. On what factor does the operating speed of the relay depend?

A. Rate of flux built up

B. Armature core air gap

C. Spring tension

D. All of these

Correct : D. All of these

27. Protective relays can be designed to respond to ___________.

A. Light intensity, impedance

B. Temperature, resistance, reactance

C. Voltage and current

D. All of these

Correct : D. All of these

28. What is the purpose of back up protection?

A. To increase the speed

B. To increase the reach

C. To leave no blind spot

D. To guard against failure of primary

Correct : D. To guard against failure of primary

29. What is the major cause of the failure of the circuit breaker?

A. Trip circuit open

B. Trip latch defective

C. Spring defective

D. All of these

Correct : D. All of these

30. Why are the isolators used?

A. Break abnormal current

B. Making under fault conditions

C. Breaking the circuit under no load condition

D. None of the above

Correct : C. Breaking the circuit under no load condition

31. The isolators used in the transmission lines are capable of breaking

A. Fault current

B. No current

C. Charging current

D. Load current

Correct : C. Charging current

32. For which among the following the current ratings are not required?

A. Circuit breakers

B. Relays

C. Isolators

D. Load break switch

Correct : C. Isolators

33. What is the making to breaking current ratio for an extra high voltage circuit breaker?

A. More than 1

B. Equal to 1

C. Less than 1

D. A negative value

Correct : A. More than 1

34. The breaking capacity of a three phase circuit breaker is given by

A. Service line voltage * rated symmetrical current in amperes * 10-6 MVA

B. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

C. 1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA

D. √2 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

Correct : B. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

35. Which of the following circuit breaker is highly reliable and has a least maintenance?

A. Oil circuit breakers

B. Air blast

C. Vacuum circuit breakers

D. SF6 circuit breakers

Correct : D. SF6 circuit breakers

36. The rating of the circuit breaker is usually determined on the basis of ____________ fault.

A. Symmetrical

B. Line to line

C. Single line to ground

D. Double line to ground

Correct : A. Symmetrical

37. Which among these circuit breakers produce the least arc energy?

A. Plain oil

B. Minimum oil

C. Air blast

D. Air break

Correct : C. Air blast

38. A thermal protection switch provides protection against what?

A. Overload

B. Temperature

C. Short circuit

D. Over voltage

Correct : A. Overload

39. What does protective relay provide?

A. Provide additional safety to the circuit breaker in its operation.

B. Close the contacts when the actuating quantity attains a certain predetermined value.

C. Limit the arcing current during the circuit breaker operation.

D. Earth or ground any stray voltage.

Correct : B. Close the contacts when the actuating quantity attains a certain predetermined value.

40. What is the main purpose of oil in oil circuit breakers?

A. Provide insulation

B. Quenching ar(C)

C. Provide cooling of contacts.

D. None of the above

Correct : B. Quenching ar(C)

41. What is the advantage of using oil as the arc quenching medium?

A. Good cooling properties.

B. High dielectric strength.

C. Acts as an insulator.

D. All of these.

Correct : D. All of these.

42. When does the arc interruption in oil circuit breaker take place?

A. Contacts apart.

B. Voltages becomes zero

C. Current goes through zero

D. All of the above

Correct : C. Current goes through zero

43. For rural electrification in India, which circuit breaker is generally used?

A. Oil

B. SF6

C. Vacuum

D. Air blast

Correct : C. Vacuum

44. Keeping in view the cost and the overall effectiveness, which of the following circuit breaker is best suited for capacitor bank switching?

A. Vacuum circuit breaker

B. Air blast CB

C. SF6

D. Oil CB

Correct : A. Vacuum circuit breaker

45. To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of

A. Low conductivity and high vapour pressure.

B. Low conductivity and low vapour pressure.

C. High conductivity and high vapour pressure.

D. High conductivity and low vapour pressure.

Correct : A. Low conductivity and high vapour pressure.

46. SF6 gas is imported in _____________.

A. Air cylinders

B. Gas cylinders

C. Liquid form in cylinders

D. Solid form.

Correct : C. Liquid form in cylinders

47. During arc extinction SF6 gas gets converted to which among these?

A. Gets decomposed to SF4 and SF2

B. Gets decomposed to S and F

C. Gets reduced to SF6

D. Gets oxidized

Correct : A. Gets decomposed to SF4 and SF2

48. What is the most important property which makes the SF6 very efficient medium for circuit breaking?

A. Is non toxic and non inflammable.

B. Has a high dielectric constant.

C. Has a high breakdown strength

D. Is highly electronegative gas

Correct : D. Is highly electronegative gas

49. What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?

A. 2 kg / cm2

B. 2.5 kg /cm2

C. 2.8 kg / cm2

D. 3 kg / cm2

Correct : C. 2.8 kg / cm2

50. What is the major drawback of using SF6 circuit breakers?

A. Sealing problems of the gas.

B. Ingress of moisture in the gas system – dangerous.

C. Deterioration of SF6 gas with time.

D. Both (a) and (b)

Correct : D. Both (a) and (b)

51. Why do the SF6 gases have an excellent heat transfer property?

A. Low gaseous viscosity.

B. High dielectric strength.

C. Higher molecular weight.

D. Both (a) and (c)

Correct : D. Both (a) and (c)

52. What is the breaking capacity of the air blast circuit breaker?

A. 5000 MVA

B. 6000 MVA

C. 7000 MVA

D. 10000 MVA

Correct : C. 7000 MVA

53. In axial blast type of CB, expansion of air takes place from ______________.

A. High pressure to low pressure.

B. Low pressure to high pressure.

C. Always in high pressure.

D. Always in low pressure.

Correct : A. High pressure to low pressure.

54. The air blast circuit breakers for 400 kV systems are designed to operate in how much time?

A. 0.1 s

B. 0.5 s

C. 50 ms

D. 100µs

Correct : C. 50 ms

55. What is the type of air blast in cross blast type CB?

A. The blast of air is along the ar(C)

B. The blast of air cuts across the ar(C)

C. Both (a) and (b)

D. None of the above.

Correct : B. The blast of air cuts across the ar(C)

56. Why is the resistance switching used in a air blast circuit breaker?

A. Reduce the magnitude of fault current.

B. Control the CB operating time.

C. Damp out the fast transient.

D. Change the fault current power factor.

Correct : C. Damp out the fast transient.

57. When using air blast circuit breaker, current chopping is a phenomenon observed when

A. A long overhead line is switched off.

B. A bank of capacitors is switched off.

C. A transformer on no load is switched off.

D. A heavy load is switched off.

Correct : C. A transformer on no load is switched off.

58. Which type of air is used in air blast circuit breaker?

A. Ionised air

B. Air free from moisture

C. Air should have least CO2

D. Air must have oil mist.

Correct : B. Air free from moisture

59. What is the maximum current upto which fuses can be used?

A. 25 A

B. 50 A

C. 75 A

D. 100 A

Correct : D. 100 A

60. What is fusing factor?

A. The ratio of current rating of the fuse to the minimum fusing current

B. The ratio of minimum fusing current to the current rating of the fuse

C. The ratio of maximum fusing current to the current rating of the fuse

D. The ratio of minimum fusing current to the voltage rating of the fuse

Correct : A. The ratio of current rating of the fuse to the minimum fusing current

61. For a current upto 10A which material is used as the fusing element?

A. Copper

B. Silver

C. Alloy of lead and tin

D. Zinc

Correct : C. Alloy of lead and tin

62. Which among these is the least expensive protection for over current in low voltage system?

A. Rewirable fuse.

B. Isolator.

C. Circuit breaker.

D. Air breaker switch.

Correct : A. Rewirable fuse.

63. Which among the following statement is true related to fuse?

A. Greater the current smaller is the time taken by the fuse to blow out.

B. Greater the current greater is the time taken by the fuse to blow out.

C. The current is directly proportion to the blow out time of fuse.

D. Is dependent on the temperature and atmospheric conditions.

Correct : A. Greater the current smaller is the time taken by the fuse to blow out.

64. How is the restriking voltage measured?

A. RMS value

B. Peak value

C. Instantaneous value

D. Average value

Correct : B. Peak value

65. What is the interrupting medium in the contactor?

A. Air at atmospheric pressure.

B. SF6 gas

C. Oil

D. All of the above.

Correct : D. All of the above.

66. Recovery voltage is the value of rms voltage that reappears across the poles of a circuit breaker before_______________

A. Restriking voltage

B. Final arc extinction

C. Rise of voltage

D. All of the above

Correct : B. Final arc extinction

67. Why is it difficult to interrupt a capacitive circuit?

A. The current has a leading power factor.

B. The restriking voltage can be high.

C. Current magnitude is very small.

D. Stored energy in the capacitor is very high.

Correct : B. The restriking voltage can be high.

68. Rate of rise of restriking voltage depend on_____________?

A. Type of circuit breaker.

B. Capacitance of the system.

C. Inductance of the system.

D. Both (b) and (c)

Correct : D. Both (b) and (c)

69. On what factor does the rate of rise of restriking voltage (RRRV) depend?

A. System voltage.

B. Circuit power factor only

C. Switching conditions

D. Both (b) and (c).

Correct : D. Both (b) and (c).

70. In a circuit breaker, the active recovery voltage depends upon which among these?

A. Circuit conditions.

B. Power factor.

C. Both (a) and (b)

D. None of the above

Correct : C. Both (a) and (b)

71. What is restriking voltage?

A. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.

B. The transient voltage that appears across the circuit breaker contacts at the end of arc extinction.

C. Both (a) and (b)

D. None of the above

Correct : A. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.

72. For a high speed circuit breaker what will the total clearing time?

A. Few minutes.

B. Few seconds.

C. 1 to 2 cycles.

D. 5 to 20 cycles.

Correct : C. 1 to 2 cycles.

73. The interrupting time of a circuit breaker is the period between the instant of _________.

A. Initiation of short circuit and the arc extinction on an opening operation.

B. Energizing the trip circuit and the arc extension on an opening operation.

C. Initiation of short circuit and the parting of primary arc contacts.

D. Energizing of the trip circuit and the parting of primary arc contacts.

Correct : B. Energizing the trip circuit and the arc extension on an opening operation.

74. In a circuit breaker, ionisation is facilitated by_________________.

A. Increase in field strength.

B. Increase in mean free length.

C. High temperature of the surrounding medium.

D. All of the above.

Correct : D. All of the above.

75. Which of the following should have low value for the contacts and their material?

A. Thermal capacity.

B. Contact resistance.

C. Thermal conductivity.

D. None of above.

Correct : B. Contact resistance.

76. The heat produced at the contact point owing to flow of electric current is least affected by_____________________.

A. Temperature of the surrounding medium.

B. Contact resistance.

C. Magnitude of electric current flowing.

D. Duration of flow of current.

Correct : A. Temperature of the surrounding medium.

77. The resistance of an electric arc can be increased by

A. Increasing the concentration of ionised particles.

B. Reducing the arc length.

C. Splitting the ar(C)

D. Increasing the arc cross section.

Correct : C. Splitting the ar(C)

78. By using low resistance method for arc extension what is the value of arc resistance?

A. Arc resistance is zero.

B. Arc resistance is high

C. Arc resistance is low

D. Arc resistance is very high

Correct : C. Arc resistance is low

79. What happens in the arc extinction using high resistance method?

A. Arc resistance is decreased with time.

B. Arc resistance is increased with time.

C. No change it remains same.

D. Arc resistance is kept zero.

Correct : B. Arc resistance is increased with time.

80. What is the arc voltage in a circuit breaker?

A. In phase with the arc current.

B. Lagging the arc current by 90°

C. Leading the arc current by 90°

D. Lagging the arcing current by 180°

Correct : A. In phase with the arc current.

81. Arcing voltage will be the least in case of

A. Carbon

B. Copper

C. Silver

D. Tungsten

Correct : C. Silver

82. How is the initiation of electric arc at the instant of contact separation caused?

A. Thermionic emission of electrons.

B. Field emission of electrons.

C. Both (a) and (b)

D. None of these.

Correct : C. Both (a) and (b)

83. The arc resistance depends on which among the following factors?

A. Cross section of the ar(C)

B. Length of the ar(C)

C. Degree of ionization

D. All of the above.

Correct : D. All of the above.

84. Which type of tripping is generally preferred for the circuit breaker?

A. Manual

B. Automatically

C. Depending on the voltage level

D. None of the above

Correct : B. Automatically

85. Which part of the circuit breaker is helpful in breaking the current?

A. Trip coil.

B. Contacts.

C. Medium

D. Handle.

Correct : B. Contacts.

86. When a fault occurs in a high voltage transmission line, what happens first?

A. Circuit breaker operates then the relay.

B. Relay operates and then the circuit breaker.

C. Relay operates, then successively the isolator and the circuit breaker.

D. Isolator operates, then successively the relay and the circuit breaker.

Correct : B. Relay operates and then the circuit breaker.

87. Upto what voltage can the liquid type HRC fuses be used?

A. 33 kV

B. 132 kV

C. 66 kV

D. 220 kV

Correct : B. 132 kV

88. What is the main advantage of using a fuse?

A. Cheapest type of protection.

B. Inverse time current characteristics.

C. Current limiting effect under short circuit conditions.

D. All of above.

Correct : D. All of above.

89. On what basis is the selection of fuse done?

A. Steady loa(D)

B. Fluctuating loa(D)

C. Both (a) and (b)

D. None of these.

Correct : C. Both (a) and (b)

90. Upto what voltage a cartridge type of fuse can be used?

A. 400 V

B. 11 kV

C. 20 kV

D. 33 kV

Correct : D. 33 kV

91. In a HRC fuse what is the time between the cut off and the final current zero called?

A. Pre - arcing time.

B. Arcing time.

C. Total operating time.

D. None of these.

Correct : B. Arcing time.

92. Which material is used in the liquid type of fuse?

A. SF6

B. Distilled water

C. Carbon tetra chloride.

D. Mineral oil / transformer oil

Correct : C. Carbon tetra chloride.

93. What is the advantage of HRC fuses over Rewirable fuses?

A. High speed operation

B. High rupturing capacity

C. No ageing effect.

D. All of the above.

Correct : D. All of the above.

94. If the strands of the fusing wire are twisted, what happens to the fusing current?

A. Increases

B. Reduces.

C. No change/ remains same

D. Depends on the value of current, increases or decreases.

Correct : B. Reduces.

95. What is the typical value of the pre arcing time?

A. 0.1

B. 0.01

C. 0.001

D. 0.0001

Correct : C. 0.001

96. Outdoor switchgear is generally used for voltage beyond

A. 11 KV

B. 33 KV

C. 66 KV

D. 132 KV

Correct : C. 66 KV

97. The least expensive protection for over current in low-voltage system is

A. Rewirable fuse

B. Isolator

C. Circuit breaker

D. Air-break switch

Correct : A. Rewirable fuse

98. Purpose of backup protection is

A. To increase the speed

B. To increase a reach

C. To leave no blind spot

D. To guard against failure of primary

Correct : D. To guard against failure of primary

99. We do not require any protection against prime mover failure in case of

A. Turbo generator sets

B. Hydro generator sets

C. Diesel engine driven alternators

D. Back pressure turbo generators

Correct : A. Turbo generator sets

100. For the protection of stator winding of an alternate against internal fault involving ground the relay used is a

A. Biased differential relay

B. Directional over-current relay

C. Plain impedance relay

D. Buchholz relay

Correct : A. Biased differential relay